1. Field of the Invention
This invention relates to cryosurgery and more particularly to cryoablation catheters comprising a fluid operating near its critical point.
2. Description of the Related Art
Cryoablation is a surgical technique for ablating tissue by cooling or freezing the tissue to a lethal degree. Cryoablation has the benefit of minimizing permanent collateral tissue damage and has applicability to a wide range of therapies including the treatment of cancer and heart disease.
A shortcoming with certain cryosurgical systems, however, arises from the process of evaporation. The process of evaporation of a liquefied gas results in enormous expansion as the liquid converts to a gas; the volume expansion is on the order of a factor of 200. In a small-diameter system, this degree of expansion consistently results in a phenomenon known in the art as “vapor lock.” The phenomenon is exemplified by the flow of a cryogen in a thin-diameter tube. The formation of a relatively massive volume of expanding gas impedes the forward flow of the liquid cryogen through the tubes.
Traditional techniques that have been used to avoid vapor lock have included restrictions on the diameter of the tube, requiring that it be sufficiently large to accommodate the evaporative effects that lead to vapor lock. Other complex cryo-apparatus and tubing configurations have been used to “vent” N2 gas as it is formed along transport tubing. These designs also contributed to limiting the cost efficacy and tube diameter.
There is accordingly a need for improved methods and systems for providing minimally invasive, safe and efficient cryogenic cooling of tissues.